PREHEAT oven to 300° F.
PLACE cream, half-and-half and vanilla extract in large saucepan. Bring to a boil; remove from heat. Add chocolate; whisk until melted and smooth.
WHISK egg yolks and 1/3 cup sugar in large mixer bowl. Gradually whisk in chocolate mixture.
POUR mixture through fine sieve into six 4-ounce ramekins or custard cups. Place ramekins in 13 x 9-inch baking dish; fill pan with hot water to 1-inch depth.
BAKE for 40 minutes or until custards jiggle slightly when pan is shaken. Cool custards in water until cool enough to handle. Remove custards from water; refrigerate for 2 hours. Cover with plastic wrap; continue to refrigerate for several hours or overnight.
PREHEAT broiler. Sprinkle 1 teaspoon sugar over tops of each custard. Place custards on baking sheet. Broil for 3 minutes or until sugar is melted and caramelized (rotate pan as needed to prevent burning). Alternately, tops can be caramelized using kitchen torch. Refrigerate for 2 hours so that the topping can harden and the custard can cool and set.